DFT calculations of the surface and the electronic structure of silicon core approximants for sensing

Silicon core approximants terminated with hydrogen, hydroxyl and methyl termination were investigated by density-functional-theory calculations within B3LYP hybrid functional formalism using 6-31G(d) Gaussian type molecular-orbital basis set. Optimized geometric structures including bond lengths and bond angles for all clusters were obtained. The electronic structures of the various clusters are calculated including density of state analysis, natural bond orbital analysis and the HOMO-LUMO orbitals analysis. The influences of the Si surface bond termination on charge transfer and local breakdown of the MO symmetry were discussed. UV-vis spectra of all the clusters mentioned above are also calculated. The g tensor for all structures are studied and discussed. All data show the SiO double bond is found to be the most probable surface structures of the Si quantum dots exposed to the atmosphere of H2O, O2 and CH3CH2OH gases. Of course it still need for further studies and verification of experiments. The investigation will provide a theoretical basis for the sensing of silicon quantum dots.